I think I love your mind for pointing out the lack of thought behind the 'soulmates first words or names' thing. I tend to find the whole idea of soulmates depressing if not horrifying really. I ran across one recently though, in the Teen Wolf fandom that is quite well thought out in the whys and hows and consequences. The story posits matching birthmarks, not words, names or even symbols, and does a decent job of world building. It kind of runs with the meta of lots of people think soulmates would be so wonderful and then figures out what happens when they engineer that into the species, only they didn't think it through enough and it doesn't turn out at all rainbows and flowers.

Keywords: dysfunctional, depressing, and dystopian.

The link, in case you're at all curious about it: Playing God